Optical system



Dec. 17, 1940. B. A. DIGGINS 2,225,039

OPTICAL SYSTEM Filed Aug. 20, 1958 BARTHOLOMEW A. DIGGINS ATTORNEY I INVENTO 23 2; -FIG.3 BY

Patented Dec. 17, 1940 OPTICAL SYSTEM Bartholomew A. Dig'glns, Irondequoit, N. Y., as-

signor to Bansch &

Lomb Optical Company,

Rochester, N. Y., a corporation of New York Application August 20, 1938, Serial No. 225,979

1 Claim.

The present invention relates to optical instruments and more particularly to inverting and.

reverting prism systems such as those used in prism telescopes or binoculars.

It has long been known that there is a loss of light at the adjacent glass-air surfaces of the prism systems of prism telescopes or binoculars and many attempts have been made to avoid that loss. These attempts have usually consisted 10 in cementing the prisms together before mounting, making complex one-piece prisms or cementing a piece of glass between the elements of the optical system. These attempted corrections have usually been failures for a number of apllj parent reasons. p

The cementing of the prisms is impractcal because the rosultant cemented combination is fragile to handle and dimcult to mount and align because of its pecuiar shape. Furthermore,

20 mounting such a cemented combination is apt to strain or even break the cement bond. Even if the strain mounting were not suiiicient to break the cement bond. it would probably hasten the deterioration of the cement.

28 The one-piece prism is obviously impractical because of the great cost of manufacture. The surfaces have to be optically flat and the angles so closely related and controlled that. 'if it is possible to make such prisms, their cost would 80. be prohibitive.

Glass plates or blocks cemented between the optical elements are impractical for both of the above reasons. These plates or blocks not only add further optical surfaces which must be 281 ground to optical precision but the angular relation of these surfaces and the length of the light path must be held to very close limits. The production of such blocks requires such high precision that the cost would far exceed the value of u} the improvement. p v

One of the objects of my invention is to provide a method of reducing. the surface-losses between two optical elements separated by an air space. Another oblect is to provide a pair a of spaced optical elements with a transparent connecting member formed in place between them. A further object is to provide a prism system in which a transparent member of moldable material is formed between the prisms and 50 in optical contact therewith. These and other objects and advantages reside in certain novel features of construction, arrangement and combination of parts as will hereinafter be more I fully set forth and pointed out in the appended I! claim.

(c1. ssss) Referring to the drawing:

Fig. 1 is an elevation of a pair of prism binoculars with parts broken away to show internal structure.

Fig. 2 is a plan view of a prism table embodying one form of my invention.

Fig. 3 is a fragmentary vertical section showing another form of my invention prior to assembly.

Fig. 4 is a side elevation of the prism combination of Fig. 3 after assembly.

Fig. 5 is a perspective view of a prism assembly embodying my invention.

One embodiment of the present invention is U illustrated in the drawing in connection with a pair of prism binoculars. These binoculars consist of two body members it and II hingedly secured together and each carrying an objective l2 at one end and an eyepiece l3 at the other. The usual focusing knob It may be provided. Within each body member is a shelf l5 to which the prism table It carrying a Form prism combination is suitably secured as, for example, by screws not shown which extend through the holes l6. This construction is well known to those skilled'in the art.

The prism table It consists of a substantially iiat plate having three spaced holes I1, l8 and i9 therethrough. As shown in Fig. 2, these holes form an isosceles right triangle, the hole ll being located opposite the hypotenuse of the triangle. One surface of the table it is recessed as indicated at 20, the recess 20 connecting the holes I! and I8, and the other side is recessed as indictaed at 2|, the recess 2| connecting the 3iholes I! and [8. The two isosceles right prisms 22 and 23 are mounted in the recesses 20 and 2i, respectively, with their hypotenuse surfaces restin}; on the table It at the bottom of the recesses. These prisms 22 and 23 are fixed in the recesses 4c by straps 24 and 25, respectively, which extend over the prisms and are secured to the prism table as, for example, by screws. 26 which are threaded into the holes 26' in the prism table It.

Ordinarily, the prisms 22 and 22 are separated 4;.- by an air space and thus there are losses by reflection at the two adjacent glass-air surfaces. According to the present invention, a transparent member indicated generally at 21 in Fig. 5 is placed in optical contact with both prisms 22 and 22 and thus eliminates the glass-air surfaces with their attendant reflection losses. This member must be clear and transparent in thick sections and-must be moldable at reasonable temperatures and pressures. Various synthetic resins such as the acrylic acid resin commercially known as Plexiglas and the vinyl resin commercially known as Vinylite may be used. Other transparent substances such as ethyl silicate can also be used.

The connecting member 21 is formed in difierent ways depending on the original condition oi! the material used, but I prefer to form it in place when the prisms 22 and 23 are mounted. Fig. 2 illustrates the construction of the prism table l6 when the material forming the member 21 is applied in a liquid state and allowed to harden. In this embodiment, the prism table i6 is provided with an inlet 28 and an outlet 29 opening into the hole ii. The two prisms 22 and 23 are secured on opposite sides of the table i6 and form closures for the ends of the hole ii. A transparent liquid is introduced through the inlet 28 until the hole I1 is entirely filled, the displaced air escaping through outlet 29. The liquid is then allowed to harden and form. the

v optical connection 21 illustrated in Fig. 5.

In the embodiment illustrated in Figs. 3 and 4, a solid plug 30 of transparent material is used. This plug 30, as shown in Fig. 3, is very slightly thicker than the table is at the recesses 20 and 2i. The plug 30 is softened either by heat or by the application of a suitable plasticizer and the two prisms 22 and 23 are pressed against the plug 30 until they seat normally in their respective recesses 26 and 2!. The prisms 22 and 23 are then secured in position by the-straps 2t and 25, respectively, and the plug allowed to harden as a connecting member as shown in Fig. 5.

In order to provide a place for the plug St to expand when it is pressed by the prisms 22 and 23, the walls of the hole i! are rounded as shown in Figs. 3 and 4 or are otherwise suitably recessed.

The choice of the two methods illustrated depends entirely on the original condition of the material used to form the member 3i. Ethyl silicate is usually a fluid and in that event the method of Fig. 2 would be used. The acrylic acid resin Plexiglas can be obtained either as a liquid or in plugs and hence either 'method could be used with this resin. Other transparent resins and mixtures of resins are well known and the three materials recited are given merely by way of example. Likewise, the various plasticizers or softening agents, and solvents to: these transparent materials are well known to those skilledin the art.

After the prisms 22 and 28 have been mounted andthe trent connecting member 2! has 5 been formed, the table i6 is mounted on the shelf i5 in such a way that the hole It is in alignment with the objective i2 and the hole It in alignment with the eyepiece it. The table it is then secured in position as is well known in 10 the art.

Fromthe foregoing, it will be apparent that I am able to attain the objects of my invention and provide a simple, practical and inexpensive system for eliminating the surface losses between 15 optical elements. While I have illustrated my invention as applied to a Porro prism system used in prism binoculars, other applications and uses are readily apparent to those skilled in the art. Various modifications can also be made 20 without departing from the spirit of my invention or the scope of the appended claim.

I claim:

In a prism system for telescopes and the like comprising a substantially flat table having three 25 spaced holes therethrough with an isosceles right angle glass prism secured on one side of said table with its hypotenuse face resting on the table so that one end extends over one of said holes and with a second isosceles right angle 30 glass prism secured on the other side of said table with its hypotenuse face resting on the table so that one end extends over the hole covered by said first mentioned prism, the other ends of the hypotenuse races of said prisms each 35 covering a separate hole in said table difierent from said first mentioned hole, said table also havin a plurality of conduits provided therein and connecting the interior of the hole covered by both of said prisms with a surface 0! said table, ,40 a clear transparent member having an index of BARTHOLQMEW A. DIGGINS. 

